Speaking as someone who studied excess courses back in the day, I still agree with the GP. There's a big difference between being able to pursue random sparks of interest (as might someone picking up a course they find interesting) and consistently studying even when you aren't necessarily inspired by the material, or when the material is so hard it stops being fun. I spend a lot of time working on projects in my spare time even today, but I can think of only one case where I worked anywhere near as hard on one of those as I did on the projects for my university's OS course, or compilers course, or etc. Even students who do regularly go above and beyond would likely struggle without the structure to A) tell them what to learn, B) give them motivation -- because of course many students who do go the extra mile are still motivated by grades, prestige, research opportunities, etc.